Typically, a light emitting diode (LED) die emits light into a full hemisphere. For some applications, such as for general room lighting, such an output can be desirable. However, for other applications, such as for display-panel backlighting, a side-to-side output emission can be required. Typically, in such applications it is desirable that the light is emitted into only a few degrees of angle relative to a display-panel viewing plane, so the light can become homogenized before exiting the backlight.
A variety of devices have been developed to condense an LEDs hemispherical emission and redirect it into sideways direction. Unfortunately, none of these prior devices perform efficiently and generally emit light into a broad exit angle, or into other unmanageable directions.
One such well-known side-emitting optical 1, element is illustrated in FIG. 1. This optical element is comprised of a lower refractive section 2, and an upper TIRing section 4. Rays, such as ray 8, that are emitted from the source 14 in a direction within 30 degrees of parallel with the optical axis 3 enter the upper TIRing section 4, whereupon they TIR from an upper surface 5 and are directed to an output surface 6. These rays then refract through the output surface 6 into a direction that is somewhat perpendicular to the optical axis 3.
Other rays, such as ray 6, that are emitted from the source 14 in a direction greater than about 30 degrees from the optical axis 3 enter the lower refractive section 2, whereupon they are incident on output surface 9. These rays refract through the output surface 9 into a direction that is somewhat perpendicular to the optical axis 3.
Yet other rays, such as ray 10, that are incident on the upper surface 5 of the upper TIRing section 4 at or near where the optical axis 3 intersects the upper surface 5, will refract through upper surface 5 into a non-side-emitting, or non-radial, direction. These rays intersect the upper surface 5 at or near the apex of the upper surface. Ideally the apex is dead-sharp, but because of non-ideal manufacturing processes the apex will have a non-zero radius of curvature, and will also be non-zero in size. Light rays such as ray 10 will refract through this section into a non-controlled, non-radial, and undesirable direction.
It is difficult to block rays such as ray 10 by installing a plug into the recess 11, because the plug will need to be in optical contact with the upper surface 5, which will destroy the TIRing property of the upper surface 5, and compromise the performance of the optical element 1. Furthermore, the plug cannot be placed into the recess and be expected to stay in place due to friction, which necessitates the use of an adhesive along upper surface 5, which will further compromise the TIRing performance of the upper surface 5 and degrade the performance optical element 1.
Because of the stray light rays, such as ray 10, the inability to block them at the upper surface 5, and the generally poor side-emission characteristics of the optical element 1, the optical element 1 is undesirable to use in many applications.